1. Field of the Invention
The present invention relates to a fuel injection system provided with a timer mechanism and a control sleeve, such as a VR pump (an inner-cam distributor type fuel injection pump provided with plungers at a rotor that rotates in synchronization with an engine, facing opposite each other in the direction of the radius of the rotor, to compress and inject fuel by causing the plungers to make reciprocal movement with the inner-cam) and a VE pump (a distributor type fuel injection pump with a rotor that rotates in synchronization with an engine being caused to make reciprocal movement itself relative to a plunger barrel by a cam disk to compress and inject fuel) and, in particular, it relates to a fuel injection system provided with a pre-stroke control mechanism.
2. Description of the Related Art
This type of fuel injection system includes the one disclosed in, for instance, Japanese Unexamined Patent Application No. S61-23832, in which a cam disk 29 is placed in contact with a roller 32 that is held by a roller ring 31. A plunger 26, which faces a plunger high pressure chamber 25, is secured to the cam disk 29 and is caused to make rotating and reciprocal movements by the cam disk 29, which rotates in synchronization with an engine. In the plunger 26, a through hole 50, through which fuel is taken into the plunger high pressure chamber 25 from a pump chamber 22 during the intake process, a distribution port 35, through which fuel pressurized in the plunger high pressure chamber 25 is delivered during the force feed process, and spill ports 51 and 52 for cutting off the fuel delivery, are formed. Fuel supplied to the plunger high pressure chamber 25 is compressed with the reciprocal movement of the plunger 26, and the fuel thus compressed is distributed with the reciprocating movement of the plungers 26.
A control sleeve 53 is externally fitted on the plunger 26 covering the spill ports 51 and 42, and by moving this control sleeve 53 in the direction of the axis, the fuel injection quantity is varied by changing the fuel force feed end timing and, at the same time, by rotating the control sleeve 53 in the circumferential direction, the start timing of fuel force feed, i.e., the length of time elapsing from the start of cam lift until the start of fuel force feed (pre-stroke), is controlled. In addition, the cam lift start timing is adjusted by varying the positional relationship between the cam disk 29 and the roller 32.
In the fuel injection system described above, because of its structural features, the fuel force feed end timing, the cam lift start timing and the fuel force feed start timing can be controlled independently of one another and a number of advantages are achieved, such as: (1) the injection pressure can be increased to reduce the generation of black smoke and NOx by setting the injection period during high load operation in the low rotation speed range or during partial load operation (partial operation, medium load operation) in a range over which the cam speed is high; (2) if it is necessary to reduce the size of the nozzle hole of the injection nozzle to conform to exhaust gas regulations, it is possible to extend the range over which cam lift is in effect during high rotation speed, high load operation, and; (3) since the injection timing can be practically modified by adjusting the fuel force feed start timing as well as adjusting the cam lift start timing, the range over which the injection timing can be adjusted freely is extended. However, since the structure described above requires that an actuator for controlling the fuel force feed start timing be provided separately, apart from an actuator for controlling the fuel force feed end timing and an actuator for controlling the cam lift start timing, the number of actuators increases, making the control more complicated and increasing the production cost.